The hallmarks of chronic inflammation and tissue fibrosis are the influx of inflammatory cells, accumulation of inflammatory mediators and increased turnover and production of the extracellular matrix (ECM). In intact lungs, high molecular weight ECM components, such as hyaluronan (HA), play a critical role in maintaining conformational integrity and water homeostasis but are considered biologically inert. However, in the setting of inflammation, the HA is degraded into lower molecular weight fragments that stimulate macrophages to produce important mediators of tissue injury and repair. Although it is known that HA fragments induce the activation of NF-kappaB, the receptor and signaling pathways responsible for HA induced gene expression have yet to be elucidated. The aim of this proposal is to characterize the signal transduction pathways involved in HA fragment induced gene expression as well as the molecular mechanisms by which IFN-gamma differentially regulates HA-induced chemokine expression in alveolar macrophages both in vitro and in vivo. We hypothesize that HA, fragments induce chemokine gene expression through toll-like receptors (TLR) via Protein Kinase C and NF-kappaB pathways, and furthermore that IFN-gamma exerts its anti-fibrotic effects by selectively altering macrophage-derived chemokine expression by ECM. This will be pursued by determining: (1) the mechanism by which MyD88 mediates HA-induced genes in macrophages, the toll-like receptor responsible for HA signaling and the effect of MyD88 deficiency on bleomycin-induced lung injury. (2) The mechanism by which HA activates Protein Kinase C as well as the mechanism by which Protein Kinase C regulates HA-induced genes and the effect of pharmacologic inhibition of Protein Kinase C on bleomycin-induced lung injury. (3) The role of co-activation in mediating the synergy between HA and IFN-gamma induced MIG expression, the role of co-repression in mediating the inhibition of HA-induced MIP-1alpha expression by IFN-gamma, and the effect of NF-kappaB p50 deficiency on bleomycin-induced lung injury. Thus, in the setting of inflammation, the ECM is not only the target of inflammation, but its breakdown products modulate the magnitude and quality of an immune response. The elucidation of the role of ECM in inflammation may lead to a better understanding of the process of fibrosis as well as to new targets for novel treatment strategies. [unreadable] [unreadable]